1. Field of the Invention
The present invention relates to apparatus for heat input into the reboiler stream of distillation or reaction distillation columns. More particularly the invention relates to the use of a single fired heater to provide heat to several reboiler streams. Most particularly the invention relates to the use of a slip stream from a reboiler stream which has been heated by a fired reboiler as a heat transfer medium to heat other reboiler streams.
2. Related Information
In fractional distillation heat must be provided to drive the boiling of the components to be separated. Generally the heat is provided by taking a portion of the bottoms from the distillation column and passing it through a heat exchanger to add heat and then recycling the heated portion of the bottoms back to the distillation column. Some amounts of heat may be added by "pump arounds" wherein the liquid from individual trays in the column are circulated through heat exchangers, but in most cases, the sole or principal source of heat input to a distillation column is through the recirculation of bottoms through a reboiler.
In a reaction distillation column there is concurrent reaction of components and separation by fractional distillation of the reaction products from the reactants. The reaction may be exothermic or endothermic. Even if the reaction is exothermic some heat must be provided to initiate the reaction and to continue to drive the separation. This heat is generally provided by a reboiler as in traditional distillation columns. Of course heat must be provided when the reaction is endothermic. In addition to the latent heat of vaporization the reboiler must also add the heat necessary to sustain the reaction.
The heat in a reboiler can be provided either from a heat exchange medium, such as steam, or by passing the bottoms material through tubes which are surrounded by flames in a fire box--a fired reboiler. The type of reboiler is dependent upon the amount of heat required and upon the temperature of the heated fluid. Generally fired reboilers are more economical when large amounts of heat are required or when temperature is high.
Plant operating complexities and difficulties increase substantially with multiple fire reboilers. One usual alternative to multiple fired reboiler is the use of a hot oil system with a single common fired heater. While a hot oil system is simpler than multiple fired reboilers it is substantially more expensive.
It is known in industry to heat a first process stream from a second process stream by indirect heat exchange to recover heat from the second that would otherwise be lost. For example heat from the overheads vapor from one column may be used to heat the reboiler of another or the heat from the bottoms product from one stream may be used to heat the reboiler of another column.
It is a feature of the present invention to provide a simple alternative to multiple fired reboilers without the expense of a hot oil system.